A semiconductor wafer having a circuit pattern formed thereon is subjected if necessary to backside polishing to regulate the thickness and then subjected to dicing into a chipped work (dicing step). In the dicing step, the semiconductor wafer is washed generally at suitable fluid pressure (usually about 2 kg/cm2) in order to remove off-cut. Then, the chipped work is fixed via an adhesive onto an adherend such as a lead frame (mounting step) and then subjected to a bonding step. In the mounting step, an adhesive has conventionally been applied on the lead frame or the chipped work. In this method, however, the adhesive layer is hardly uniformly applied, and the application of the adhesive requires a special device and is time-consuming. Accordingly, a dicing die-bonding film for retaining a semiconductor wafer via an adhesive in the dicing step and providing a chip-bonding adhesive layer necessary in the mounting step has been proposed (see, for example, JP-A 60-57642).
The dicing die-bonding film described in JP-A 60-57642 supra comprises an adhesive layer arranged releasably on a substrate material. That is, a semiconductor wafer retained by the adhesive layer is subjected to dicing, and the substrate material is stretched to release the resulting chipped works together with the adhesive layer therefrom, and each chipped work is recovered and then fixed via the adhesive layer to an adherend such as a lead frame.
The adhesive layer in this kind of dicing die-bonding film is desired to exhibit good retention of the semiconductor wafer as well as good releasability of the chipped work together with the adhesive layer from the substrate material after dicing in order to prevent problems such as dicing infeasibility and erroneous dimensions. However, these two features are hardly balanced. Particularly, when the adhesive layer requires high retention in a system of dicing a semiconductor wafer with a rotating round blade, it is difficult to obtain a dicing die-bonding film satisfying these features.
To overcome this problem, a wide variety of modifications have been proposed (see, for example, JP-A 2-248064). JP-A 2-248064 proposes a method of facilitating pickup of chipped works, which comprises sandwiching a UV radiation-curing pressure-sensitive adhesive layer between a substrate material and an adhesive layer and then curing it with UV rays after dicing to reduce the adhesion between the pressure-sensitive adhesive layer and the adhesive layer thereby releasing the layers from each other.
However, there is the case where even by this modification method, good balance between retention during dicing and releasability after dicing is hardly attained by the adhesive layer. For example, when a large chipped work of 10 mm×10 mm or more is to be obtained, easy pickup of the chipped work is infeasible with a general die bonder because of the large area of the work.
To solve this problem, the present applicant applied a dicing die-bonding film excellent in balance between the retention of a work during dicing and releasability of its diced chipped work together with a die-bonding adhesive layer (JP-A 2002-299930). Even in the pickup step using this dicing die-bonding film, a system of using a general dicing pressure-sensitive film is adopted. That is, the dicing die-bonding film is stretched to a certain extent, and the dicing die-bonding film below a chipped work to be picked up is raised or rubbed in a dotted or linear state to facilitate the release of the chipped work from the dicing die-bonding film, and the chipped work is picked up by upward vacuum adsorption. The dicing die-bonding film in the application supra can achieve excellent pickup.
In recent years, however, the works (semiconductor elements) are rendered thinner with spread of IC cards etc., and the chipped works are easily deformed (pliable) upon pickup by the technique described above, and the peel angle of the dicing die-bonding film to the chipped work tends to be reduced. As a result, the peeling strength is increased to hinder pickup.
The mechanism of pickup of thin chipped works is approximately estimated as follows: That is, when the thin chipped works are to be picked up, the dicing die-bonding film is raised with a raising pin to facilitate release, upon which the works are thin and poor in rigidity so that the edge of the works is deformed to make the peel angle between the dicing die-bonding film and the works lower than in the case of conventional thick works having rigidity, thus increasing the peeling strength to hinder pickup.